Historically, oxygen-sensitive products have been packaged and shipped in either glass or metal containers for delivery to the consumer. These containers have essentially zero gas permeability and, as such, the oxygen-sensitive products are able to remain fresh for an extended period of time.
There is a growing desire to package certain products such as, for example, food and beverage products, in various plastic (e.g., PET, HDPE, PP, etc.) containers, wrapping, and other packaging articles. Compared to glass or metal packaging, plastic packaging is typically cheaper, more resistant to breakage, and more flexible (if desired). Conventional plastics, however, have generally functioned poorly at blocking oxygen passage relative to other available materials, such as glass or metal. The permeability of conventional plastics to oxygen transmission can result in short product shelf life, especially for products that are sensitive to degradation when exposed to oxygen.
To reduce gas transmission of a plastic packaging material, a passive barrier may be used to hinder the passage of a gas, e.g., oxygen. For example, in a multi-layer bottle, the inner and outer layers may be made of PET, while the center layer is a different material with passive barrier properties such as, for example, ethylene vinyl alcohol (EVOH). However, layers of dissimilar materials often do not adhere well to one another, and an adhesive between the layers may be required to prevent delamination. The clarity of the packaging material may be reduced when a passive barrier material is used, and the multi-layered material may be more difficult to recycle.
Oxygen-scavenging materials, which reduce or deplete the oxygen in an environment, have been incorporated into plastic containers in an attempt to maintain a low level of oxygen within the container, thereby extending the shelf life of the product. These plastic containers, however, have typically suffered from one or more deficiencies such as loss of adhesion, delamination, presence of off tastes or odors in products packaged therein, poor clarity, unsuitable cost (e.g., material, storage, and/or transportation costs), insufficient oxygen-scavenging capacity and/or shelf life, and inefficient or untimely activation of oxygen scavenging. Due to such deficiencies, for example, glass still predominates over plastics in juice and beer bottling.
What is needed in the marketplace is an improved oxygen-scavenging polymer for use in articles such as packaging, wrapping and storage articles.